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+# Protocol Buffers - Google's data interchange format
+# Copyright 2008 Google Inc. All rights reserved.
+# https://developers.google.com/protocol-buffers/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+# * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+# * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# This code is meant to work on Python 2.4 and above only.
+
+"""Contains a metaclass and helper functions used to create
+protocol message classes from Descriptor objects at runtime.
+
+Recall that a metaclass is the "type" of a class.
+(A class is to a metaclass what an instance is to a class.)
+
+In this case, we use the GeneratedProtocolMessageType metaclass
+to inject all the useful functionality into the classes
+output by the protocol compiler at compile-time.
+
+The upshot of all this is that the real implementation
+details for ALL pure-Python protocol buffers are *here in
+this file*.
+"""
+
+__author__ = 'robinson@google.com (Will Robinson)'
+
+
+from google.protobuf.internal import api_implementation
+from google.protobuf import message
+
+
+if api_implementation.Type() == 'cpp':
+ from google.protobuf.pyext import cpp_message as message_impl
+else:
+ from google.protobuf.internal import python_message as message_impl
+
+# The type of all Message classes.
+# Part of the public interface.
+#
+# Used by generated files, but clients can also use it at runtime:
+# mydescriptor = pool.FindDescriptor(.....)
+# class MyProtoClass(Message):
+# __metaclass__ = GeneratedProtocolMessageType
+# DESCRIPTOR = mydescriptor
+GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType
+
+
+def ParseMessage(descriptor, byte_str):
+ """Generate a new Message instance from this Descriptor and a byte string.
+
+ Args:
+ descriptor: Protobuf Descriptor object
+ byte_str: Serialized protocol buffer byte string
+
+ Returns:
+ Newly created protobuf Message object.
+ """
+ result_class = MakeClass(descriptor)
+ new_msg = result_class()
+ new_msg.ParseFromString(byte_str)
+ return new_msg
+
+
+def MakeClass(descriptor):
+ """Construct a class object for a protobuf described by descriptor.
+
+ Composite descriptors are handled by defining the new class as a member of the
+ parent class, recursing as deep as necessary.
+ This is the dynamic equivalent to:
+
+ class Parent(message.Message):
+ __metaclass__ = GeneratedProtocolMessageType
+ DESCRIPTOR = descriptor
+ class Child(message.Message):
+ __metaclass__ = GeneratedProtocolMessageType
+ DESCRIPTOR = descriptor.nested_types[0]
+
+ Sample usage:
+ file_descriptor = descriptor_pb2.FileDescriptorProto()
+ file_descriptor.ParseFromString(proto2_string)
+ msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0])
+ msg_class = reflection.MakeClass(msg_descriptor)
+ msg = msg_class()
+
+ Args:
+ descriptor: A descriptor.Descriptor object describing the protobuf.
+ Returns:
+ The Message class object described by the descriptor.
+ """
+ attributes = {}
+ for name, nested_type in descriptor.nested_types_by_name.items():
+ attributes[name] = MakeClass(nested_type)
+
+ attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor
+
+ return GeneratedProtocolMessageType(str(descriptor.name), (message.Message,),
+ attributes)